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Title: Combination of photocatalytic andphotoelectro-Fenton/citrate processes for dye degradationusing immobilized N-doped TiO2 nanoparticles and a cathodewith carbon nanotubes: central composite design optimization
Author: Alireza Khataee Hadi Marandizadeh Behrouz VahidMahmoud Zarei Sang Woo Joo
PII: S0255-2701(13)00171-2DOI: http://dx.doi.org/doi:10.1016/j.cep.2013.07.007Reference: CEP 6319
To appear in: Chemical Engineering and Processing
Received date: 6-4-2013Revised date: 10-6-2013Accepted date: 19-7-2013
Please cite this article as: A. Khataee, H. Marandizadeh, B. Vahid, M. Zarei, S.W.Joo, wCombination of photocatalytic and photoelectro-Fenton/citrate processes fordye degradation using immobilized N-doped TiO2 nanoparticles and a cathode withcarbon nanotubes: central composite design optimization, Chemical Engineering andProcessing (2013), http://dx.doi.org/10.1016/j.cep.2013.07.007
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Research highlights:
• Hybrid photocatalytic and photoelectro-Fenton processes for dye degradation
• Doping of commercial TiO2 nanoparticles with nitrogen
• Immobilization of carbon nanotubes on carbon paper to fabricate a cathode
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Combination of photocatalytic and photoelectro-Fenton/citrate processes for dye
degradation using immobilized N-doped TiO2 nanoparticles and a cathode with
carbon nanotubes: central composite design optimization
Alireza Khataee a,*, Hadi Marandizadeh a, Behrouz Vahid b, Mahmoud Zarei c, Sang
Woo Joo d,**
a Research Laboratory of Advanced Water and Wastewater Treatment Processes,
Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz,
Iran
b Department of Chemical Engineering, Tabriz Branch, Islamic Azad University, Tabriz,
Iran
c Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz,
Iran
d School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, South
Korea
* Corresponding author (communicator)
E–mail address: [email protected] ([email protected])
Tel: +98 411 3393165; Fax: +98 411 3340191
** Corresponding author
E–mail address: [email protected]
Tel: +82 53 810 1456
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Abstract
In this report, commercial TiO2 nanoparticles were doped with nitrogen by a manual
grinding method using urea. The prepared catalyst was characterized by X-ray diffraction
(XRD), diffuse reflectance spectra (DRS), and transmission electron microscopy (TEM).
N-doped TiO2 was immobilized on ceramic plates by methyl tri-methoxy silane. Next,
multi-walled carbon nanotubes (CNTs) were stabilized on carbon paper to fabricate the
cathode. Scanning electron microscopy (SEM) was employed to confirm stabilization of
the CNTs. The prepared cathode and immobilized catalyst were utilized for the
degradation of C.I. Direct Red 23 (DR23) by the photoelectro-Fenton (PEF) process in
the presence of citrate (Cit) combined with a photocatalytic process. The coupled
PEF/Cit/N-TiO2 process could be performed under visible light, not only due to the
formation of iron-citrate complexes, but also because of the incorporation of nitrogen to
the crystalline structure of TiO2 and the generation of TiO2 complexes with
electrogenerated H2O2. Results demonstrated that the degradation efficiency of DR23 (20
mg/L) using the identical operational conditions, followed a decreasing order of:
PEF/Cit/N-TiO2 > PEF/Cit > PEF > EF > N-TiO2. Eventually, a model was developed by
the central composite design (CCD) method, describing the degradation efficiency as a
function of the operational parameters.
Keywords: Carbon nanotubes; TiO2 nanoparticles; Photoelectro-Fenton process;
Response surface methodology; Photocatalytic process.
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1. Introduction
Various branches of industry, particularly textile industries, discharge remarkable
amounts of synthetic dyes (up to 10%) into the environment during their production and
consumption. Small amounts, below 1 mg/L, of these dyes cause unfavorable color in
water and affect its transparency, as well as the solubility of gas in it. Furthermore, dyes
and their degradation products are carcinogenic, toxic, and resistant to treatment by
biodegradation or physicochemical techniques [1, 2]. Hence, their conversion to less
hazardous or complete mineralization to compounds, such as CO2 and water, is essential
from an environmental viewpoint [3, 4].
Titanium dioxide (TiO2) can absorb UV light to generate electron-hole pairs. Then,
reactive oxygen species (ROS), particularly hydroxyl radicals, are generated by photo-
stimulated reactions on TiO2 surface (Eqs. (1-6)) [5-8]. Thus, complete mineralization of
pollutants can occur by UV/TiO2, which is one of the advanced oxidation processes
(AOPs) [9, 10].
TiO2 → e− + h+ (1)
e− + O2 (ads) → •O2−
(ads) (2)
e− +H+ (ads) → •H (ads) (3)
•O2−
(ads) + H+ → HOO• (4)
2HOO• → H2O2 +O2 (5)
H2O2 +•O2−
(ads) → •OH + OH− +O2 (6)
Doping of TiO2 with nitrogen improves its photocatalytic activity in the visible light
spectrum due to nitrogen incorporation into the TiO2 crystalline structure, which reduces
band gap energy between valence and conduction bands [11, 12]. N-doped TiO2 (N-TiO2)
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can be produced by manual grinding of TiO2, with urea serving as the source of nitrogen
[6]. Immobilized TiO2 particles have both economical and practical benefits in
comparison to the suspension form, including no need for separation of TiO2 particles
after treatment and proper penetration of light into the solution [13, 14]. Characteristics
of ceramic plates, such as high surface area and stability, make it suitable as a TiO2
support [15].
Refractory organic pollutants have been treated efficiently; exploiting
electrochemical advanced oxidation processes (EAOPs), such as electro-Fenton (EF) and
photoelectro-Fenton (PEF) processes, from water [16-19]. In these techniques, in-situ
production of hydrogen peroxide by the reduction of dissolved oxygen at the cathode
eliminates its risky transportation and storage (Eq. (7)) [20, 21]. Ferric or ferrous ions (at
catalytic concentrations) are dissolved in the solution and Fe3+ is reduced to Fe2+ (Eq. (8))
[21, 22]. Therefore, Fenton’s reaction (Eq. (9)) can occur in the solution to form hydroxyl
radicals, which can unselectively oxidize pollutants in the medium [16].
O2 + 2H+ + 2e− → H2O2 (7)
Fe3+ + e− → Fe2+ (8)
Fe2+ + H+ + H2O2 → Fe3+ + •OH + H2O (9)
Carbon nanotubes (CNTs) have large surface area, mechanical strength, electrical
conductivity, and wide utilizable potential [23, 24]. Therefore, applying them in the
fabrication of the cathode leads to increased production of H2O2 when compared to other
materials, such as activated carbon or bare graphite [25, 26].
In the presence of citrate anions (Cit3-), iron species can react with them to generate
various iron-citrate complexes [27]:
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Fe2+ + Cit3- ↔ Fe(II) (Cit)¯ (10)
Fe3+ + Cit3- ↔ Fe(III) (Cit) (11)
The •OH radicals are also produced in the medium by a reaction between
Fe(II) (Cit)¯ and H2O2 [27]:
Fe(II) (Cit)¯ + H2O2 → Fe(III) (Cit) (OH)¯ + •OH (12)
Moreover, visible light can be absorbed by the following Fe3+ complexes to generate
Fe2+, which can take apart in the catalytic cycle of iron in the PEF process (Eqs. (13) and
(14)) [27- 29].
Fe(III) (Cit) (OH)¯ + hν → Fe2+ + 3-HGA•2- (13)
2Fe(III) (Cit) + hν → Fe(II) (Cit)¯ + Fe2+ + 3-OGA2- + H+ + CO2 (14)
Where 3-HGA•2- and 3-OGA2- are 3-hydroxo-glutarate radical and 3-oxo-glutarate,
respectively [27].
The effect of operational parameters on the efficiency of the most treatment methods
was performed by one factor at a time method requiring an unreasonable number of
experiments. Central composite design (CCD), which is one of the response surface
methodologies (RSM), was used to model the various treatment processes [30-31]. An
adequate number of experiments are required to develop a mathematical model for
predicting the degradation efficiency and for finding the direct and interactive effects of
the operational parameters [32].
The aim of this study is to investigate the degradation of C.I. Direct Red 23 (DR23)
by combination of photocatalytic and photoelectro-Fenton/citrate processes using N-TiO2
nanoparticles and a cathode with CNTs under visible light instead of ultraviolet
irradiation. The central composite design approach is applied, not only for describing the
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degradation efficiency of coupled process (PEF/Cit/N-TiO2), but also for determining
individual and interactive effects of operational parameters, including initial
concentration of DR23, Fe3+ to Cit3- molar ratio, applied current, and process time.
2. Materials and methods
2.1. Chemicals
C.I. Direct Red 23 (DR23) (Mw = 813.72 g/mol and λmax = 497 nm) was obtained from
Boyakhsaz Company (Iran), for use as a model anionic di-azo dye. Multi-walled CNTs,
with inner and outer diameters of 6 nm and 22 nm, respectively, were purchased from
Cheap Tubes Inc. (USA). The transmission electron microscopy (TEM) image of CNTs
(shown in Fig. 1) was carried out on a Zeiss EM 900 (Germany). Commercial TiO2
nanoparticles (PC-500) containing 99% anatase phase (Millennium, Belgium), with a
specific surface area of 9.82 m2/g, and crystalline mean size of 8 nm were utilized in
experiments. Distilled water was used throughout the experiments. A solution of PTFE
(60% W/W) and carbon paper were obtained from Electrochem (Iran) and Pars
Hydropasargad (Iran), respectively. Ceramic plates were purchased from Kashi Tabriz
(Iran). All other materials were obtained from Merck, Germany.
2.2. Immobilization of prepared nitrogen-doped TiO2 nanoparticles and fabrication of
the CNTs-PTFE cathode
Mechanical mixing of urea with TiO2 nanoparticles (4:1 weight ratio) was applied to
prepare N-doped nanoparticles. The obtained mixture of nanoparticles was annealed
under air atmosphere at 400 ºC with a heating rate of 10 ºC per minute and cooled at
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room temperature. The resulting light yellow powder was crushed in an agate mortar. X-
ray diffraction (XRD) was performed on a Siemens D5000 (Germany). Fig. 2 shows
peaks at 2θ = 25.3º, 37.8º, and 48.1º, which corresponded to the anatase crystalline form
of TiO2 [15]. Diffuse reflectance spectra (DRS) were carried out on a Scinco S-41200c
(South Korea) and demonstrated that the absorption of N-TiO2 shifted to the visible
region (Fig. 3). N-TiO2 nanoparticles were immobilized on the ceramic plate using
modified silica (methyl tri-methoxy silane) as a hydrophobic binder using the sol-gel
based method [33]. CNTs were stabilized on carbon paper using polytetraflouroethylene
as the hydrophobic binder [26]. The SEM images of the ceramic plates and carbon paper
before and after immobilization of N-TiO2 and CNTs, respectively, are shown in figs. 4
and 5.
2.3. Instrument and experimental procedure
Fig. 6 illustrates the experimental set-up for the PEF/citrate/N-TiO2 process. A DC
power supply was used to carry out experiments with a Pt anode (surface area of 11.5
cm2) and a CNTs cathode (25 mm diameter and 0.6 mm thickness). Sodium hydroxide
and sulfuric acid were added to the solution to adjust pH, which was determined using a
pH-meter (Metrohm 654, Switzerland). Sodium sulfate (0.05 M) was used as background
electrolyte. A fluorescent lamp (6W, GK-140, China) served as the visible light source
and was placed in a glass sleeve and immersed directly in a batch cubic reactor (2500
mL). The absorbance (A) of the solution was measured at maximum wavelength of DR23
(λ max = 497 nm) using a UV-Vis spectrophotometer (Lightwave S2000, England). The
ceramic plates with immobilized N-TiO2 nanoparticles covered the inner walls of the
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cubic reactor. In each run, 2000 mL of DR23 of known initial concentration containing
specific amounts of ferric chloride and sodium citrate was poured into the reactor. Then,
the DC supply and visible light source were turned on. The operational parameters ranges
and experimental conditions of each run are presented in Tables 1 and 2, respectively.
Degradation efficiency (DE%) at specific time intervals during the process was defined
as the percentage ratio of decolorized DR23 to its initial absorbance (A0) at λ max (Eq.
(15)).
100)A
AA((%)DE0
0 ×−
= (15)
It should be noted that the absorbance of ferric chloride, sodium sulfate, sodium
citrate, and a solution of a mixture of all of them were negligible in comparison to DR23
solution at 497 nm.
3. Result and discussion
3.1. Comparison of N-TiO2, EF, PEF, PEF/citrate, and PEF/citrate/N-TiO2 processes
in DR23degradation
Fig. 7 illustrates that under the same operational conditions, after 90 min of treatment
by various processes under visible light, the decreasing order of the DE% of DR23 (20
mg/L) was:
PEF/citrate/N-TiO2> PEF/citrate > PEF> EF> N-TiO2
It should be noted that the pH and amounts of Fe3+ were optimized in the EF
containing processes, as 3 and 0.3 mM, respectively. According to Eq. (7), an acidic pH
of 3 was appropriate for production of H2O2. However, when the pH is lower than 3, the
two side reactions (Eqs. (16) and (17)), decrease the produced amount of H2O2. In basic
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pHs, Fe(OH)3 precipitates out of solution, preventing regeneration of the Fe2+ ions by
decreasing dissolved Fe3+ and partially coating the surface of the cathode [16, 25, 26].
H2O2 + 2H+ + 2e¯ → 2H2O (16)
2H+ + 2e¯ → H2 (17)
When the Fe3+ concentration increased from 0.1 to 0.3 mM, the oxidation rate of
DR23 was enhanced, resulting from a further reduction of Fe3+ to Fe2+ (Eq. (8)), which
can take part in the Fenton reaction (Eq. (9)). However, at high Fe3+ concentration (from
0.3 up to 0.8 mM), it reacts with H2O2 to produce the less active hydroperoxyl radical
(HO2•) (Eqs. (18) and (19)). Besides, by enhancing the amount of Fe2+, it acts as hydroxyl
radical scavenger (Eq. (20)), which is the most efficient oxidizing agent (Eq. (9)) [16, 34,
35].
Fe3+ + H2O2 → [Fe-OOH]2+ + H+ (18)
[Fe-OOH]2+ ↔ Fe2+ + HO2• (19)
Fe2+ + •OH → Fe3+ + OH¯ (20)
The experimental results revealed that DR23 degradation was enhanced in the
presence of visible light irradiation, citrate, and N-TiO2 by the coupled PEF/Cit/N-TiO2
process. It can be explained by the regeneration of Fe2+ ions by the reductive photolysis
of Fe(III)-Citrate complexes (Eqs. (13) and (14)) and electron transfer from the photo-
excited dye molecule, which was excited by visible light, to ferric ions (Eqs. (21) and
(22)) [29, 36].
Dye + hν → Dye* (21)
Dye* + Fe(III) → Fe(II) + Dye+ (22)
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The generated Fe2+ ions can participate in the Fenton’s reaction (Eq. (9)) to form
hydroxyl radicals by reaction with electrogenerated H2O2 [16]. Furthermore, extra
hydroxyl radicals are produced by the reaction of Fe(II) (Cit)¯ with H2O2 (Eq. (12)) [27].
Moreover, the N-TiO2 absorption spectrum shifts to visible light, not only due to the
incorporation of nitrogen atoms to the anatase crystalline structure [11, 12], but also
because of the formation of surface complexes of H2O2/TiO2. Next, photo-induced
electron transfer from these complexes to the conduction band of TiO2 leads to
decomposition of H2O2 under visible light, generating more •OH radicals, which result in
further degradation of DR23 [37]. As a consequence, PEF/Cit/N-TiO2 was chosen to
perform the subsequent experiments.
3.2. Development and validation of the central composite design model
The effect of four main factors, including the initial concentration of DR23 (X1),
Fe3+ to Cit3- ratio (X2), applied current (X3), and process time (X4), on the degradation of
DR23 by PEF/Cit/N-TiO2 was investigated by the CCD approach. Thirty-one
experiments were carried out, comprising of 7 replications at the center point, 16 cube
and 8 axial points. The independent variables (Xi) were coded as xi for statistical
calculations by the following equation:
(23)
Where X0 is the amount of Xi at the center point and Xδ is the step change [38]. Table 1
shows the ranges and levels of operational (independent) variables. Minitab 15 software
⎟⎠⎞
⎜⎝⎛
δ−=XXXx 0i
i
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was utilized for analyzing of experimental results [31, 39]. A second order polynomial
equation was applied to relate the dependant (DE%) and independent variables.
jik
ji1ij
k
1i
2iiii
k
1ii0 XXbXbXbb%DE ∑+∑+∑+=
≤≤== (24)
Where bi, bii and bij are the regression coefficients for linear, squared and interaction
effects, respectively. By substituting of the coefficients values in Eq. (23), which were
estimated by Minitab 15 software, the following equation was obtained:
Y = 79.777 - 1.781X1 + 6.085X2 + 5.122X3 + 14.6381X4 + 2.6337 21X - 0.2344 2
2X -
7.9969 23X - 4.1063 2
4X + 1.3259X1X2 +2.3566X1X3 - 2.8809X1X4 + 0.1641X2X3 -
2.2384X2X4 - 4.0541X3X4 (25)
The 4-factor CCD matrix, experimental data, and calculated data for DE% are
presented in Table 2. The correlation of determination (R2) was 0.976, which indicated
the proper ability of the model for predicting of DE%.
Analysis of variance (ANOVA) is another way to test the significance and adequacy
of the CCD model [40]. ANOVA subdivides the variation of the results to variation
associated with the model and experimental error, respectively, demonstrating if the
variation from the model is significant or not when compared with residual error. F-value
is the ratio of the mean square of the model and residual error. When F-value is greater
than the tabulated value for a definite number of degrees of freedom in the model at a
significance level of α, the model is suitable for describing the results. The obtained F-
value was 69.52, which is considerably more than the tabulated F (2.352) at 95%
significance, proving the adequacy of the CCD model [31].
To calculate the effect of each factor on the response, Pareto analysis [39] was used:
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100
1
2
2
×⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜
⎝
⎛
=∑
=
n
ii
ii
b
bP
(26)
As shown in Fig. 8, the three main effective parameters on response (DE%) were the
process time (52.83%), interactive effect of the Current-Current (15.77%), and Fe3+ to Cit
molar ratio (9.11%).
3.3. Response surface and counter plots for PEF/Cit/N-TiO2 process
Three-dimensional response surface and two-dimensional counter plots were plotted
based on the CCD model to study the effect of independent variables on the response.
Fig. 9 illustrates the effect of Fe3+ to citrate ratio and process time on DE% for initial
DR23 concentration of 20 mg/L and applied current of 300 mA. Citrate concentration
varied from 0.075 to 0.9 mmol/L at Fe3+ optimal amount (0.3 mmol/L). As shown in Fig.
9, the optimum ratio was determined to be 2.5. This can be explained by Fe2+
regeneration and more •OH radicals production from iron-citrate complexes (Eqs. (12)-
(14)). Moreover, the formations of these complexes prevent the production of stable
carboxylate complexes with Fe3+. Carboxylates are intermediates of azo dye degradation
[27, 28]. However, when the citrate concentration was more than 0.15 mmol/L, DE%
decreased due to the scavenging effect of citrate on hydroxyl radicals (Eq. (27)).
Furthermore, by enhancing of Fe(III)-Citrate complexes generation, quantum yield of Fe2+
regeneration decreased [27, 28, 41].
Cit3- + •OH → 3-HGA•2- (27)
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Fig. 10 shows DE% as a function of the applied current and process time at Fe3+ to
citrate ratio of 2.5 and DR23 concentration of 20 mg/L. Enhancement of DR23
degradation by increasing the applied current results from greater formation of H2O2 and,
consequently, hydroxyl radical production [16]. Fig. 11 shows the effect of the initial
DR23 concentration and process time for Fe3+ to citrate ratio of 2.5 and applied current of
300 mA. Under the same operational parameters, the identical hydroxyl radicals are
generated, which react with more DR23 molecules and their degradation intermediates,
leading to less DE% [35].
4. Conclusions
Degradation of DR23 by a combination of photocatalytic and PEF processes under
visible light was investigated in a batch reactor using a cathode with CNTs and a Pt
anode. N-TiO2 nanoparticles were prepared and immobilized on ceramic plates by sol-gel
based method. Then, citrate was added to the DR23 solution. The incorporation of
nitrogen to the TiO2 crystalline structure to form N-TiO2, generation of H2O2/TiO2 and
iron-citrate complexes leads to perform PEF/Cit/N-TiO2 process under visible irradiation.
The coupled process was more efficient than the PEF/Cit, PEF, EF, and photocatalytic
processes. The effect of operational parameters, including initial concentration of DR23,
Fe3+ to Cit3- ratio, applied current, and process time on the degradation efficiency was
investigated using the CCD approach, which required reasonable number of experiments.
A CCD model was developed for properly describing the degradation efficiency (R2 =
0.976) and determining of the individual and interactive effects of variables on the
response (DE%).
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Acknowledgments
The authors thank the University of Tabriz, Iran for all the supports provided.
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Figures captions: Fig. 1. TEM image of the used CNTs.
Fig. 2. XRD pattern of N-doped TiO2.
Fig. 3. DRS spectra of undoped TiO2 and N-doped TiO2.
Fig. 4. SEM image of the ceramic plates (a) before and (b) after immobilization of N-
doped TiO2.
Fig. 5. SEM image of the carbon paper (a) before and (b) after immobilization of CNTs.
Fig. 6. Experimental set-up for PEF/Cit/N-TiO2 process.
Fig. 7. Degradation efficiency (DE%) for a 20 mg/L DR23 solution at room temperature,
I = 100 A, pH = 3, [Na2SO4]0 = 0.05 mol/L, [Fe3+]0 = 0.3 mmol/L, [citrate]0 = 0.15
mmol/L; (■)N-TiO2, (×) EF, (▲) PEF, (∆) PEF/citrate, (●) PEF/Cit/N-TiO2.
Fig. 8. Pareto graphic analysis.
Fig. 9. The response surface and contour plots of the decolorization efficiency (%) as the
function of Fe3+ to citrate molar ratio and reaction time (min).
Fig. 10. The response surface and contour plots of the decolorization efficiency (%) as
the function of applied current (mA) and reaction time (min).
Fig. 11. The response surface and contour plots of the decolorization efficiency (%) as
the function of initial dye concentration (mg/L) and reaction time (min).
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Figures
Figure 1
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Figure 2
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Figure 3
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(a)
(b)
Figure 4
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(a)
(b)
Figure 5
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Figure 6
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Figure 7
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Figure 8
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Figure 9
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Figure 10
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Figure 11
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Tables
Table 1- Experimental ranges and levels of the independent test variables.
Ranges and levels Variables -2 -1 0 +1 +2 Initial dye concentration (mg/L) (X1) 10 15 20 25 30 Fe3+ to Citrate ratio (X2) 0.5 1.5 2.5 3.5 4.5 Applied current (mA) (X3) 100 200 300 400 500 Reaction time (min) (X4) 10 30 50 70 90
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Table 2- The 4-factor central composite design matrix and the value of response function
(DE (%)). Fe3+/ Citrate
CR (%)
Run [DR23]0 (mg/L)
Applied current (mA)
Reaction Time (min) Experimental Predicted
1 -1 -1 -1 -1 45.33 39.26 2 +1 +1 +1 +1 85.33 87.39 3 +1 +1 -1 -1 57.32 59.81 4 0 0 -2 0 64.46 67.37 5 -1 -1 -1 +1 90.48 86.88 6 -2 0 0 0 92.21 93.74 7 +1 -1 +1 -1 60.73 53.39 8 0 0 0 0 80.36 79.54 9 0 0 0 0 79.65 79.54
10 -1 +1 +1 +1 90.35 92.01 11 0 0 0 0 80.99 79.54 12 0 0 +2 0 92.33 91.71 13 -1 +1 -1 -1 56.11 52.90 14 0 0 0 +2 95.51 92.49 15 -1 +1 +1 -1 70.45 69.55 16 0 0 0 0 78.65 79.54 17 +1 +1 +1 -1 75.42 76.46 18 -1 -1 +1 +1 95.12 94.58 19 0 0 0 0 78.21 79.54 20 0 0 0 -2 30.31 33.94 21 +1 +1 -1 +1 81.32 79.69 22 +1 -1 +1 +1 79.23 80.54 23 0 0 0 0 80.99 79.54 24 0 +2 0 0 60.94 57.89 25 0 0 0 0 79.58 79.54 26 +1 -1 -1 +1 70.65 72.85 27 -1 +1 -1 +1 80.32 84.31 28 -1 -1 +1 -1 50.88 55.91 29 +2 0 0 0 87.53 86.61 30 0 -2 0 0 33.75 37.40 31 +1 -1 -1 -1 35.65 36.75
